Astronomical perspective: a very large body, very far away, next to very small one close by.

Astronomy Picture of the Day 🪐@apod.shinyakato.dev · 11h ago

🔭 Jupiter and the Moons Credit & Copyright: Chirag Upreti ap261012

Just up my street! Who can’t fail to learn about the origins of one’s mother tongue a fascinating prospect. To judge from the preview, David Anthony is a most engaging & readable writer.

Princeton University Press@princetonupress.bsky.social · 2d ago

"A fascinating look into the origins of modern man."—Publishers Weekly The new Princeton Classics edition of David W. Anthony's The Horse, the Wheel, and Language, with a new preface by the author, is out now! Read a free preview: buff.ly/Isccyky #Anthropology #Language

If you look at astronomy textbooks, it's pretty much impossible to show the trajectory of the Earth and moon around the Sun. Does the moon orbit the Sun or Earth? #physics #astronomy rjallain.medium.com/why-do-textb...

Why Do Textbooks Lie About the Moon’s Orbit Around the Earth?

Everyone knows about the Sun, Earth and moon. As the Earth rotates on its axis, the Sun moves through the sky and this defines a day. The…

rjallain.medium.com

Thomas Young, who was the first person to explain & demonstrate the properties of light in terms of wave motion also was first to explain that supernumerary arcs are a consequence of waves interference.

Astronomy Picture of the Day 🪐@apod.shinyakato.dev · last wk.

🔭 Supernumerary Rainbows over New Jersey Credit & Copyright: John Entwistle ap261004

You couldn’t get a finer view of the fabled ‘seven colours’ of a rainbow than this, always bearing in mind that it’s colours blend into one another, unlike those that can be produced with a prism or diffraction grating

Michael Faint@ansolasoir.com · 2w ago

South Uist, 2019 #otd

Sound is a wave so diffracts wherever it encounters an object or an opening. With few exceptions, almost every sound we hear consist of a collection of wavelengths. Short wavelengths are diffracted much less than longer ones, so low frequency sounds remain audible when source is blocked.

Effects of diffraction first noted by F.M.Grimaldi c.1665. Thoroughly investigated by Newton c 1675 with his usual phenomenal attention to detail and measurement. He accepted that water waves diffract but refused to accept that the phenomenon is due to wave nature of light.

Lunar & solar coronas are not rare but they are seldom as complete and well defined as this one. Note to self : when out & about, look up at the sky not down at my shoes!

Nereide@drnereide.bsky.social · 3w ago

This is a stunning lunar corona, visible in Death Valley. A corona is an optical phenomenon you may see when thin clouds partially veil the Sun or the Moon. Photo: Arpan Das Source: epod.usra.edu/blog/2021/08... 🔭🧪⚛️ #sciart #science #optics

Marin Mersenne, Minim friar, died 1 Sept 1648. He was the first person to discover experimentally how the frequency of a vibrating wire is related to its physical characteristics, to measure the speed of sound (by echoes & gunfire), and to determine the least pitch audible to humans is 16Hz.

Hermann v Helmholtz, born 31 Aug, 1821, not only the foremost authority on the optics of the human eye during latter half of 19th C., he was also the leading authority on the perception of sound and its relationship to music. Author of “On The Sensations Of Tone” & “Treatise on physiological optics”

This is a very clear example of a rainbow feature often ignored by casual observers: the sky enclosed by the arc is filled by light reflected by rain drops. Very obvious here because the rain is illuminated by the rosy light of a setting sun, light that is deficient in blues & greens

Betty Utility@bettyutility.bsky.social · 2mo ago

Not particularly convincing picture of a rainbow a few minutes ago. No Richard Of York Gave Battle In Vain 🌈🚫

The bluish fringe just beyond the reddish umbra may be due to sunlight that has passed though the earth’s ozone layer. Ozone strongly absorbs longer wavelength light, which gives the gas its characteristic bluish tinge. Often Noticeable at zenith during twilight.

Dan Chibnall@bookowl.bsky.social · 2mo ago

One of my best shots of the lunar eclipse tonight. No edits or filter. IPhone 16 Pro and a small Meade telescope. More shots tomorrow!

As a variation on the hackneyed theme of the sound of falling trees in the absence of a listener, have you ever asked yourself the same question about rainbows? Can there be a rainbow if there is no one to see it?

An excellent example of a double rainbow that shows very clearly important features of a rainbow that one should look out for: well defined colours in primary arc, together with supernumerary arcs, the dark band between primary and secondary and colour reversal of secondary arc.

Iñaki de Miguel Díaz :verified_aroace: 🔻:neurodiversity:@imigueldiaz.masto.es.ap.brid.gy · 2mo ago

Mastodon :aroaceheart: #rainbow #doublerainbow #summer2026

Colanders are so passé. The shape of the hole is immaterial as long as the distance to the screen is a least 110 times hole diameter. First explained by J.Keppler in 1600. He named these pinhole images "figurationes lucis ".

Gringos on eclipse safari in the Wimbledon Common savannah

I imagine that a fair number of novice astronomers, having purchased eclipse spectacles, will be dismayed at how tiny the solar disc is, no larger than the finger nails of one’ little finger held at arm’s length.

Important to note that (a) the distance between hole & screen must be at least 110 hole diameter for a clear image, and (b) under those conditions the shape of the hole plays no part. Any shape projects clear image of the sun.

Dr. James H. Gundlach@pecanjim.bsky.social · 2mo ago

When you don’t have the glasses you can take a piece of cardboard and cut about a quarter inch hole in it and when the eclipse starts hold the cardboard so the sun shines through the hole then watch where the sun shines through the hole and you can see the spot of sunlight, it will show the eclipse.

For all the recommendations to view the upcoming eclipse using colander, the use of a sieve or crossed fingers to project eclipse image is nothing new. See "Problemata" Book 15, sec 11, a work attributed to Aristotle c. 350BC, but likely by his followers.

Bees are sensitive to near u.v. and insensitive to the red end of the spectrum, so in theory can see uv rainbows (but not rosy sunsets?). Diagram from p. 274 of my vade mecum of optics "Seeing the Light, Optics in Nature, Photography, Colour, Vision and Holography" by D.Falk, D.Bril. D.Stork.

Multispectral rainbow photos by Andrew Steele. These three images are of the same bow using i.r. and u.v. filters. The central portion is of the visible light bow, below this is the infrared bow and above it is the ultraviolet bow. Newton, of course was unaware of these invisible radiations.

The reason that one can't see indigo is the spectrum is because it isn't there! Newton added indigo & orange to his original description of 5 spectral colours in order to make the number up to 7 in accordance with his belief that Pythagorean musical numerology applies to light.

@tonofwillywillies.bsky.social · 2mo ago

Nope. Still can't find the alleged indigo in Roy B Giv.

SOLAR ECLIPSE: Earth and Moon both orbit the Sun in the same direction, but at this point of their orbits Earth is travelling faster than the Moon. Hence the Moon’s shadow moves across Earth’s surface from west to east as the Earth overtakes the Moon.

I've just published a detailed video covering how to observe and photograph the deep #PartialsolarEclipse and the #Perseids #MeteorShower on 12th August 2026. Timestamps for each part are in the description box. Watch here: youtu.be/ZTwRaAbYvag

If you are interested in rainbows, mirages, halos etc then you will find Stanley Gedzelman's "Wonders of the atmosphere" www.stanrenaissanceman.com/BOOKS/WONDER...

For a thorough explanation of mirages see aty.sdsu.edu/mirages/miri...

An inferior mirage. Requires air layer next to the ground warmer than that further up (here a hot runway). This causes light that skims the ground to refract upwards reaching observer from below eye level. What appears water is refracted skylight, that can be mistaken for a pool.

Mary McIntyre@marymcintyreastro.bsky.social · 2mo ago

Today I caught these awesome aircraft #mirages at #OxfordAirport! Both #aircraft were #DiamondDA42 #TwinStar, 1st was reg: G-OATB, 2nd was G-LHXD. Photos were taken with a #Canon1100D + #Sigma 400mm zoom lens, hand-held hence the video being a bit wobbly! #HeatHaze #Aviaton

This trompe l’oeil demonstrates the role of shadows in our perception of depth/position: tinyurl.com/ycktbmdn

3D Zebra Stripe Crosswalk in Iceland Slows Traffic with Stunning Optical Illusion

The new experimental 3D crosswalk in Iceland is a pedestrian crossing meant to help slow traffic and enhance safety for those crossing the road.

tinyurl.com

Shadows among the most fascinating optical phenomena you are likely to encounter daily. A shadowless world might be very disorientating and certainly less interesting.

Shadows are an important clue to the position of an object with relation to the ground. Cover up the “shadow” in each of these photos.